The present invention relates to a shadow mask for forming a thin film electroluminescent pattern by means of a vapor growth method, a method of manufacturing a thin film electroluminescent display apparatus using the shadow mask and a thin film electroluminescent display apparatus, and more particularly to a shadow mask used for forming a thin film luminescent pattern having different luminous colors for fine pitches, a method of manufacturing a color thin film electroluminescent display apparatus using the shadow mask and a color thin film electroluminescent display apparatus.
As one structure of color thin film electroluminescent display apparatuses, as shown in FIG. 7, a pixel having different luminous colors (for example, a green luminous layer 5, a blue luminous layer 6 and a red luminous layer 7) is placed on a transparent support substrate 1 in a two dimensional matrix, and one of them, there is an apparatus for realizing a color display, in which different organic luminous materials are used for each color pixel and each color is independently emitted without using a color filter and so forth. In order to form an organic electroluminescent layer in an organic electroluminescent display apparatus having such a structure, it is necessary to form respective different organic electroluminescent films for different regions corresponding to luminous colors. For this, usually, shadow masks for luminous colors (for example, green, blue and red) are prepared, and to form electroluminescent films of each color is conducted while exchanging the shadow masks. However, in this method, it is necessary to prepare three shadow masks, and in addition, it is also necessary to conduct exchange work as many as times of the number of the masks. In order to avoid this complexity, as disclosed in JP-A-227276-1996, there is a method of forming a film in which the number of a mask to be used is one, and shadow masks are successively moved in each step of forming a luminous layer. In this method, using a shadow mask 9 as shown in FIG. 8, in which opening sections 9a are arranged in an oblique direction, a red luminous layer, a green luminous layer and a blue luminous layer are individually evaporated by successively moving this shadow mask on a substrate 1 along an arrow shown in the figure.
FIGS. 9(a)-(d) are cross sectional views showing steps, in order, of manufacturing an organic electroluminescent display panel in accordance with this method. At first, after anodes 2 are formed on a transparent support substrate 1, a hole transporting layer 4 is formed on an entire surface of a pixel formation area. And, after opening sections 9a of a shadow mask 9 are positioned to the anodes 2, a method such as evaporation is applied to a first organic electroluminescent medium such as a green luminous layer 5 to form a film with a thickness of about 10-100 nm (FIG. 9(a)). A section of the opening sections 9a of the shadow mask 9 is at a right angle to a main surface of the shadow mask 9, and each opening section 9a thereof has size corresponding to one of each luminous color element as shown in FIG. 9.
Next, as shown in FIG. 9(b), after the shadow mask 9 is shifted from a position shown in FIG. 9(a) on the left side for a distance of one luminous element, a film with a predetermined film thickness is formed of a second organic electroluminescent medium such as a blue luminous layer 6. Next, as shown in FIG. 9(c), the opening sections 9a of the shadow mask 9 are positioned to a remaining part of the luminous element, and a film with a predetermined film thickness is formed of a third organic electroluminescent medium such as a red luminous layer 7.
After three colors of organic electroluminescent luminous layers are formed, cathodes 8 are formed thereon as shown in FIG. 9(d).
In a color organic thin film electroluminescent display apparatus manufactured in such a manner, a voltage 5-20 V is usually applied between the anodes and the cathodes which constitute a desired pixel to flow a current through the organic electroluminescent layers, and an arbitrary pattern is radiated to conduct a display.
In the above-mentioned conventional method of forming the color thin film electroluminescent display apparatus, since the shadow masks for a kind of the luminous colors are prepared and exchange of the masks is conducted every time when the luminous layer of each color is formed, there was a problem that a process was complicated. Also, in the method wherein the shadow masks are moved every time when the luminous layer is evaporated, since it is necessary to provide a mechanism for moving the masks in an evaporation device, the apparatus is complicated. Moreover, since positioning has to be conducted every time when the shadow masks are exchanged or moved, it is difficult to maintain positioning accuracy between luminous layers of each color and between wafers, whereby there was a problem that it became to be difficult to manufacture the apparatus with good accuracy and high repeatability.
Furthermore, in the conventional method of forming the electroluminescent display apparatus, during the exchange or movement of the shadow masks, there is a possibility that the shadow masks come into contact with the organic electroluminescent thin film that has been formed previously, and an alien substance occurs and damage of the organic electroluminescent thin film occurs, whereby a problem occurs which introduces a lowering of display quality of the electroluminescent display apparatus due to the damage of the electroluminescent thin film and attachment of the alien substance to the organic electroluminescent panel.
Also, in the conventional shadow masks, a pattern of the opening sections has been fined in order to obtain a fine pattern. In this case, however, if a plate thickness of the shadow masks is thick, the thickness makes a shade and a fine pattern of thin film cannot be obtained. Accordingly, the thickness of the shadow masks has to be thin. However, if the thickness is made to be thin, the strength of the shadow masks is lowered and handling thereof becomes to be difficult, whereby there is a problem that the shadow masks break when they are actually used.